Communication apparatus



Feb. 20, 1968 Filed Sept. 25, 1964 DJmSCmMORE COMMUN I CATION APPARATUS 2 Sheets-Sheet 1 "Ir II I I 22 II I I II II I I II I II I H r' II r I6 I I II I DRIVE-N PULSER [26 ADDER I: N- TAPPED DELAY LINE I I 27 3o 28 IEI I I I \32 42 H 3 k n l L III I 34 I I K46 I I2 r 36 I DELAY J I ENCODER I I AUDIO 38. M00. L401 I I I 08C I l INPUT I- I 44 I I I I I & II 45 I FIG I I I I I? I 383$: I I I I ADDER ISII I MOD. I L I L "I I FILTER E I I Ir I 66 ,72 74 we II7 I I 7B I I MIXER IF DETECTOR m j lIIiAu-rAPPEo DELAY LINE Z1 I H I I 6V n 32I I I II I I I LOCAL I p80 I I OSCILLATOR I DECODER l 70 I 88 I I L I n n I k 321 I CODE 1 I 2 NPUT I 2 l l I ADDER I I I 89 P86 653 1 AUDIO I PASS AMPLIFIER \35 FILTER 87 INVENTOR.

DON L. SCHNMKWWE ATTORNE Y Feb. 20, 1968 D. SCIDMORE 3,370,126

COMMUNICATION APPARATUS Filed Sept. 25, 1964 2 Sheets-Sheet 2 DRWEN O 26 PULSER 34 1 1 l I 48 RAMP /5|54 SCHGMIDT 53354 oN E s oT TRI GER m FI 3 GENERATOR CIRCUIT VIBRATOR I I 57 RESET F56 REsET |2 t I L -J AUDIO 3 INPUT SIGNAL 36 LOW- PASS n-TAPPED DELAY LINE FILTER n 3 Fin-m. 180 /89 fl I 86 AUDIO 8? 93 \-'AMPLIFIE4 15%? 93' K90 a? Io" 83 [-85 ADD LOW 5 9l/ PASS 9 TRACTOR FILTER ADDER 8| FIG. 6

e H RAMP GENERATOR INPUT 36 H t l9 RAMP GENERATOR OUTPUT 46-60 'X SCHMIDT TRIGGER OUTPUT 8| t as MULTIVIBRATOR OUTPUT INVENTOR x DON L. SCIDMORE FIG. 4 I yww/ f ATTORNEY United States Patent 3,370,126 COMMUNICATION APPARATUS Don L. Scidmore, Seattle, Wash, assignor to Honeywell Inc.. a corporation of Delaware Filed Sept. 23, 1964, Ser. No. 398,610 7 Claims. (Cl. 1791.5)

ABSTRACT OF THE DISCLOSURE A security transmitting and receiving system utilizing a tapped delay line wherein predetermined taps of the delay line are added together to produce apparent noise. The apparent noise signal is received and decoded by a further delay line which provides a time inverse of the original tapped delay line. The signals transmitted are pulse position modulated and the frequency of the information is determined by the delay line characteristics.

The invention This invention is related to data handling and communication systems and is particularly directed to systems of this general class for processing information existing in an analog state. This invention is further directed to communication systems utilizing a transmission mode, method and apparatus which is not subject to unauthorized detection and which may be operable under substandard operating conditions as might be occasioned by noise and intentional interference.

Accordingly, as will be seen from the description set forth below, I have provided data handling apparatus and a method of operation for processing data existing in an analog state which provides a high degree of security from unauthorized use of the data and a high degree of accuracy in the handling of such data whereby undesired signals "whether present intentionally or unintentionally are substantially ineffective with respect to the quality of the information contained in the data being processed.

Briefly, my invention is comprised of apparatus which characterizes an analog signal for further processing or handling according to a predetermined pattern whereby selected portions of the analog signal are superimposed on the signal. A further means is utilized to decharacterize the signal whereby the original analog signal may be detected in the characterized signal to provide the original analog signal information.

It is therefore an object of this invention to provide a novel and improved communication system for processing and handling analog signals.

A further object of my invention is to provide an improved transmitter for use in an analog data system.

Another object of my invention is to provide an improved receiver for use in an analog data handling systerm.

A further object of my invention is to provide improved analog signal characterizing apparatus.

A still further object of my invention is to provide an improved method of characterizing analog signal information for processing and handling.

Another object of my invention is to provide an analog data communication system wherein a pair of matched filters are utilized to characterize and decharacterize an analog signal.

A still further object of my invention is to provide an improved security communications system.

These and other objects will become apparent from a consideration of the appended specification, claims, and drawing in which:

FIGURE 1 is a block diagram of a radio communication transmitter embodying the principles of my invention;

FIGURE 2 is a block diagram of a radio communication receiver embodying the principles of my invention and which may be utilized with the apparatus of FIG- URE l to provide a communication system;

FIGURE 3 is a block diagram of a portion of the apparatus shown in FIGURE 1;

FIGURE 4 is a family of curves illustrating the operation of the apparatus shown in FIGURE 3;

FIGURE 5 is a block diagram of a modification of the signal decharacterizing apparatus shown in FIGURE 2; and

FIGURE 6 is a family of curves illustrating typical wave forms of the signals appearing at the indicated portions of FIGURES 1, 2, 3 and 5.

Referring now to FIGURES 1, 2 and 6 of the drawing, there is shown in FIGURE 1, a pulse position modulator indicated generally by reference character 29 which is associated with a signal characterizing filter means indicated generally by the reference character 13 which is further connected to radio transmitting apparatus indicated generally by reference character 45 whereby an analog signal, for example an audio signal, may be characterized and radiated for transmission to remote locations. In FIGURE 2 a receiver, indicated generally by reference character 59, is shown connected to a signal decharacterizing filter means indicated generally by reference character 77, which is in turn connected to suitable means for further processing a decharacterized signal to provide a replica of the audio analog input signal to the apparatus of FIGURE 1.

Pulse position modulator 29 includes a driven pulser 10 having an input terminal 27. The output of driven pulser 10 is connected to an input terminal 28 on an added 14 through conductor 26 and to an input terminal 34 on a delay modulator 12 through conductor 32 and terminal 30 on conductor 26. Delay modulator 12 has a further input terminal 38 adapted for connection to a suitable source of analog signal (indicated as an audio signal, not shown) through conductor 36. The output of delay modulator 12 is connected to a further input terminal 42 on adder 14 through conductor 40.

Signal characterizing means 13 includes 'an N-tapped delay line 16 having an input terminal 21 connected to the output of adder 14 through conductor 19. Delay line 16 is provided with a predetermined number of taps, e.g. 1, 2, 3-k(nl), n. The last tap, n, in the delay line is connected to input terminal 27 on driven pulser 10 through conductor 11. An encoder 18 is shown having a plurality of input and output terminals corresponding in number to the number of taps (n) on delay line 16. Encoder 18 may be provided with means (not shown) for providing continuity between selected corresponding input and output terminals, for example an electronic switch responsive to a code input (not shown) which may be supplied to encoder 18 through conductor 44 and code input terminal 47. The electronic switches may conveniently be considered as single pole single throw switches connected intermediate corresponding input and output terminals. It may thus be seen that selected signals appearing on predetermined taps of delay line 16 will appear at the output of encoder 18 according to the status of the switches. In one embodiment of my apparatus, approximately half of the switches were closed so that a so-called pseudo random coded output appeared on the output terminals of encoder 18. Each of the output terminals of encoder 18 is shown connected through suitable conductors to an adder 20. Adder 20 may be comprised of a plurality of parallel summing resistors connected to provide an output on conductor 15. The signals applied to the predetermined summing resistors in adder 20 appear 'as a serial output on conductor 15.

Transmitter 45 is shown including a modulator 22 which is connected to an oscillator 24 which in turn is connected to an antenna 46 for radiating a signal in accordance with the signal present on conductor 15 connected to an input terminal 17. Radio transmitter 45 may be one of many forms of transmitting equipment known to those skilled in the art.

Referring to FIGURE 2, a radio receiver 59 is shown comprised of an antenna 66 connected to a filter 62 which is in turn connected to a mixer 66 which is adapted to receive a signal from a local oscillator 70. The output of mixer 66 is connected to conductor 61 through an IF stage 72, a full wave detector 74 and a low pass filter 76.

Signal decharacterizing filter means 77 is shown comprised of a delay line 78, a decoder 80 and an adder 82. Delay line 78 is shown having n taps corresponding to the taps on delay line 16 in FIGURE 1 and it may be noted that the taps are connected in an inverse manner, with respect to delay line 16, to decoder 80 through suitable conductors. Decoder 80 may comprise apparatus as described above in connection with encoder 18 and it is desired that a coded input supplied from a source (not shown) to conductor 88 and terminal 79 provide 'a predetermined pattern With approximately one-half the switches closed corresponding to the pattern supplied to encoder 18. The output of decoder 80 is supplied to adder 82 through suitable conductors and an output from adder 82 appears at conductor 81. Adder 82 may be comprised of a plurality of summing resistors for simultaneously adding all signals appearing at its input terminals from delay line 78 connected through decoder 80. The output of adder 82 is connected to a low pass filter 84 which includes a converter from pulse position modulation to pulse width modulation of some type such as a multivibrator or flip-flop in an input stage thereof, through coriductor 81 and input terminal 83. The output of low pass filter 84 is connected to input terminal 87 of an audio amplifier 86 through conductor 85. An audio analog signal for use by suitable output signal utilization means appears at conductor 89 connected to audio amplifier 86.

A family of curves on FIGURE 6 is provided to illustrate the signals appearing at various portions of the apparatus shown in FIGURES 1 and 2 and reference characters corresponding to the conductors on which the signals are present have been applied to facilitate reference to FIGURES 1 and 2.

It may be noted that signal characterizing filter 13 and signal decharacterizing filter 17 comprise 'a matched filter of the general class described by Turin in an article An Introduction to Matched Filters, IRE Transactions on Information Theory, June 1960.

It should further be noted that the code input appearing on conductors 44 and 88 may be continuously simultaneously varied in a predetermined pattern by suitable means (not shown) to further increase the security of the data transmission.

A detailed diagram of a portion of FIGURE 1 is shown on FIGURE 3 inwhich the several elements of which delay modulator 12 is comprised are shown in block diagram in connection with the associated portion of the apparatus of FIGURE 1. FIGURE 4 shows a family of curves which are illustrative of the operation of the delay modulator 12 shown in FIGURE 3. In FIGURE 3, driven pulser is shown having an input terminal 27 connected to conductor 11 upon which appears a train of pulses of predetermined frequency as will be set forth below. Driven pulser 10 is connected to adder 14 through conductor 26 and to a ramp generator 48 that is connected to input terminal 34 on delay modulator 12 through conductor 32. Ramp generator 48 is connected to an input terminal 54 on a Schmidt trigger circuit 50 through conductor 51. Trigger circuit 50 is connected to input terminal 154 on a one shot multivibrator 52 through conductor 53. The output of multivibrator 52 appears on conductor 55 which is in turn connected to reset terminals 57 and 56 on ramp generator 48 and trigger circuit 50 respectively. Conductor 55 has a further terminal 58 that is connected to conductor 40 which is in turn connected to input terminal 42 on adder 14. A further input terminal 38 on delay modulator 12 is shown connected to conductor 36 which may be energized from a suitable source of analog data indicated as an audio input signal. As may be seen from a consideration of the family of curves in FIGURE 4, delay modulator 12 provides, in combination with the train of pulses supplied by driver; pulser 10 and adder 14, an analog to digital conversion of the analog signal appearing on conductor 36. In FIG- URE 4A a pulse indicated at time T is supplied from driven pulser 10 and passes through adder 14 to conductor 19 and is simultaneously applied to ramp generator 48 which initiates a sweep as indicated on curve 413. At the time the amplitude of the sweep voltage generated in generator 48 reaches the amplitude of the analog audio signal supplied to trigger circuit 50, an output pulse indicated by t on FIGURE 4C is provided and is applied to one shot multivibrator 52. The output thereof is indicated by curve 4D and is a pulse of substantially constant amplitude and duration. The output of multivibrator 52 then passes through adder 14 and appears as a serial pulse following the pulse from driven pulser 10 which is displaced in time in accordance with the analog audio signal amplitude supplied to trigger circuit 50. Simultaneously, the ramp generator 48 and trigger circuit 50 are reset to the initial condition and, upon reception of a further pulse from driven pulser 10, the operation described above Will be repeated.

Operation Referring now to FIGURES l, 2, 3, 4 and 6, the operation of the illustrated embodiment will be described. Operation with no analog signal input to conductor 36 will first be considered. It may be seen, at this time, that a pulse from driven pulser 10, as indicated on curve 11 (FIGURE 6) is circulated through a circuit including conductor 26, adder 14, delay line 16 and conductor 11. Additionally, each output of driven pulser 10 causes the delay modulator 12 to derive and supply a similar pulse, only delayed in time, to tapped delay line 16 through conductor 40 and adder 14. The time delay of delay line 16 may be selected to be equal to or less than the inverse of twice the highest frequency which may be present in an analog signal. For example, an audio signal of 5 kilocycle spectral content would indicate a time delay line of microseconds. It therefore follows that the total delay time for time delay line 16 should be equal to or less than 100 microseconds for an analog signal of this spectral content. The delay time between the taps may be equally divided. The number of equally spaced taps on delay line 16 is determined by the spectral bandwidth desired in the characterized signal. In the example noted above, a one microsecond time delay between taps in the 100 microsecond delay line was observed to be sufficient to maintain an adequate signal to noise ratio for satisfactory processing of an analog signal of the indicated. frequency. The nominal width of the individual pulses: must be somewhat less than the time interval between the taps on delay line 16. Hence, with no signal applied. to conductor 36, a continuous train of equally spaced pulse pairs of a predetermined frequency is supplied to signal characterizing filter means 13 and a repetitive train of serial pulses is transmitted from radio transmitter 45. The pulse train configuration appearing on output conductor 17 of signal characterizing filter means 13 as a'result of each input pulse on conductor 21 is determined by the status of the individual electronic switches in encoder 18 in determining which of the output taps of delay line 16 are connected to adder 20. As a pulse passes through delay line 16 from tap 1 to tap n, a corresponding pulse is produced at the output of adder 20 to provide a spectrum spreading effect. Since the input to the signal characterization filter 1 3, with no analog signal applied to audio input conductor 36, is pulse pairs, the output appearing on conductor 15 to the modulator 22 consists of the repetitive overlapping sum of two identical pulse trains, one delayed with the respect to the other, where each individual train is that which would be developed by a single pulse input to the signal characten'zation filter 13. It should also be noted at this point that driven pulser may be provided with suitable inhibiting means (not shown) which are responsive to the train of pulses referred to above to inhibit driven pulser 10 during interpulse intervals so that the only frequency determining element which may affect driven pulser 10 is delay line 16.

Assuming now that 'an audio analog signal is supplied to terminal 38 on delay modulator 12, it may be seen from a consideration of FIGURES 3 and 4 that the second pulse is generated at a predetermined time after a pulse has been generated by driven pulser 10. This pulse appears on conductor 40 and is applied to terminal 42 on adder 14 and follows the pulses circulating through delay line 16 by a time interval determined by the amplitude of the audio signal. The maximum time interval must be less than the time interval between the pulses circulating through delay line 16. As mentioned previously with the second pulse present, as indicated by the curves 19 on FIGURE 6, two pulses separated in time are applied to delay line 16 and each time a tap that is connected through encoder 18 to adder 20 is energized by one of the pulses, a pulse output will appear on conductor from adder to provide a mixing of the two trains of pulses. The varying amplitude 'audio input signal causes this mixed output to vary continuously as a result of the varying delay in the output of the delay modulator 12. The serial mixing of the trains of pulses results in an output signal having substantially no variation in 'amplitude or pulse repetition frequency despite the varying pulse train configuration as a result of the audio analog signal input and provide a composite characterized signal that may be used to modulate a transmitter. The general waveform of the characterized signal may be seen on curves 15, 46-60 and 61 on FIGURE 6.

The signal is received in receiver 59 and the output is applied to input terminal 71 on delay line 78 in decharacterizing filter means 77. It may be noted that the taps on delay line 78 are numbered in an inverse order with relation to the taps on delay line 16 in FIGURE 1. A signal output indicated by curve 81 on FIGURE 6, corresponding to curve 19 thereon will appear at the output of adder 82. The noise appearing at a relatively constant amplitude is a result of a signal passing through delay line 78 and the sum of any pulses present on the taps connected through decoder 80 to adder 82 results in the relatively constant level of noise shown. When a signal which has been characterized by a code corresponding to the code present in decoder 80 is present in delay line 78 wherein each of the taps correspond in time position to pulses present in the pulse train at output 15 of the signal characterizing means 13 as a result of one pulse applied to the input 21 of signal characterizing filter means 13 in FIGURE 1, the potential appearing at each of the taps is simultaneously added in adder 82 and a relatively large pulse will appear at the output as indicated by curve 81. Pulse pairs with varying spacing will appear at the output 81 as a result of the dual pulse position modulation input to signal characterization means 13. This signal is then applied to a low pass filter which serves to convert the pulse position modulation output to an analog output indicated by curve 85 on FIGURE 6 corresponding to the analog input represented by curve 36 on FIGURE 6. It has been noted that distortions of a characterized signal may occur which will destroy some of the pulses generated by signal characterizing filter means 13 without substantially impairing the operation of 6 the apparatus as the amplitude of the pulses, as shown on curve 81, will merely be reduced.

While I have described the operation of my apparatus as utilizing a coding arrangement wherein approximately half of the switches are closed to provide a pseudo random signal, other forms of coding may occur to those skilled in the art upon becoming familiar with the principles of my invention.

The apparatus of FIGURE 5 is an embodiment in which the signal to noise ratio of the output of decharacterizing filter means 77 is increased. In this embodiment, the taps corresponding to the predetermined code are connected in common to a conductor 91 that is connected to an input terminal 94 of a l adder 100. The signal appearing at the output of adder 100 is substantially the same as indicated by reference character 81 on FIGURE 6. The remainder of taps in decoder 80 are connected in common to a conductor 93 that is connected to an input terminal 94 on a 0 adder 90. A signal, substantially the mirror image of curve 81 on FIGURE 6 with reduced amplitude of the large pulses appears at the output of zero adder 90. Adder is connected to an input terminal 99 on a subtractor 92 through conductor 98 and adder 100 is connected to an input terminal 97 on subtractor 92 through conductor 96. The signals from adders 90 and 100 are subtracted and appear on conductor 81 which is connected to terminal 83 on low pass filter 84. The subtraction of the two signals results in a substantial reduction of the noise in the intervals between the correlated signal pulses.

While I have shown and described a preferred embodiment of my invention, it is to be understood that my invention is limited only by the terms of the appended claims.

I claim:

1. Data handling apparatus for providing security coded signals comprising in combination:

(1) a source of pulse position modulated signals;

(2) signal characterizing filter means, including tapped delay line means with a period greater than the period between adjacent pulses from said source of signals operable to simultaneously add delayed selected portions of said signal from prior time periods to itself by summing the signal outputs of predetermined taps of said delay line to provide a resultant output having random characteristics with respect to said signal; and

(3) output means connected to said filter means and adapted to be connected to output utilization means.

2. Data handling apparatus for transmitting analog data between remotely disposed locations comprising, in combination:

(1) a source of pulse position modulated signals;

(2) signal characterizing means including tapped delay line means with a period greater than the period between adjacent pulses from said source of signals, connected to be energized by said source of signals, and operable to add delayed selected portions of said signal from prior time periods to itself by summing signals appearing on predetermined taps of said delay line to provide a resultant output having random characteristics with respect to said pulse position modulated signals;

(3) transmitter means connected to said signal characterizing means and being adapted to transmit a further signal representative of the output of said signal characterizing means to remotely disposed locations;

(4) at least one remotely disposed receiving means operable to provide an output in response to said further signal;

(5) signal decharacterizing means connected to the output of said receiver means; and

(6) signal utilization means connected to the output of said signal decharacterizing means.

3. In apparatus of the class above described, a filter for detecting a coded signal representative of analog data comprising, in combination: V

(1) an n tap delay line having an input terminal adapted for connection to a source of coded signal;

(2) first and second adders;

(3) circuit means connecting code determining selected taps on said delay line to said first adder;

(4) circuit means connecting the remainder of the taps on said delay line to said second adder; and

(5) subtracting means connected to said first and second adders.

4. Data handling apparatus for processing analog data comprising, in combination:

(1) a source of analog data;

(2) a first signal characterizing filter means, including an )1 tap delay line, an adder and circuit means connecting predetermined taps on said delay line to said adder;

(3) a source of signal pulses having a frequency the inverse of which is greater than the time period delay between adjacent taps of said delay line;

(4) means, connected to said source of analog data, said first filter means and said source of signal pulses, for providing a further signal, the frequency of which is determined by said first filter means, comprised of a plurality of pairs of pulses, one of each of said pairs of pulses being proportionally displaced in time from the other of said pulses in accordance with the magnitude of said analog data;

(5) circuit means connecting aid last named means to the delay line in said first filter means;

(6) means responsive to the output of the adder in said first filter means for propagating the output of first filler means to at least one receiving means;

(7) a second signal decharacter'izmg filter means including an n tap delay line, an adder and circuit means connecting like predetermined taps on said delay line to said adder, said filter means being adapted to extract said further signal from the output of said receiving means;

(8) signal converting means connected to the output of said second filter means, said signal converting means being adapted to provide a signal proportional to said analog data to an output utilization means.

5. The apparatus of claim 4 in which the circuit means connecting the predetermined taps on the delay lines to the adders in said first and second filter means are comprised of n switching means.-

6. The apparatus of claim 5 in which means responsive to a common source of coding signal are operative tocontrol the switching means to provide a predetermined pattern.

7. The apparatus of claim 5 in which at least n/ 3 and less than n/ 6 of the taps on the delay lines are connected to the adders in the first and second filter means.

References Cited UNITED STATES PATENTS 2,401,405 6/1946 Bedford 178-69.5 2,542,700 2/ 1951 Peterson '3329 2,926,217 2/1960 Powell 1791.5 3,025,350 3/1962 Lindner 179-1.5

WILLIAM C. COOPER, Primary Examiner.

R. P. TAYLOR, Assistdnt Examiner. 

